Many cities are attempting to conserve water by reducing the amount used in each toilet flushing. One approach is to apply a vacuum to the toilet bowl outlet near the beginning of each flushing to suck out water and debris to flow into a drain pipe. One old patent, Boyle U.S. Pat. No. 380,854, issued Apr. 10, 1888, describes a vacuum assisted toilet, where the bowl outlet includes upper and lower traps that are always sealed against the passage of air. The presence of two traps can allow all water from the toilet bowl to be siphoned into the drain, and allow sewer gas to leak through the toilet bowl into the environment, A vacuum assisted toilet which avoided possible loss of all water in the toilet bowl while effectively using the applied vacuum, would be of considerable value.